Physicists link quasicrystals to superconductivity and more | MIT News

In exciting research into an intriguing class of materials called quasicrystals, MIT scientists and colleagues have discovered a relatively simple, flexible way to create new atom-thin versions that can be adapted to critical events. A recent report at work problem NatureThey describe doing it to make materials exhibit superconductivity and so on.

This research introduces a new platform to not only learn more about quasicrystals, but also to explore exotic phenomena that are difficult to study but have important applications and lead to new physics. For example, a better understanding of superconductivity, the passage of electrons through a material with no electrical resistance, will allow for more efficient electronic devices.

This work brings together two previously unconnected fields: quasicrystals and twisttronics. The latter is the specialty of Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT and author of the new paper. Nature Paper, whose breakthrough in „magic-angle” graphene began the field in 2018.

„It’s quite extraordinary that the field of twisttronics is making unexpected connections with other areas of physics and chemistry, in this case the beautiful and fascinating world of quasiperiodic crystals,” says Jarillo-Herrero, who is affiliated with MIT’s Materials Research Laboratory. MIT Electronics Research Laboratory.

Make a turn

Twisttronics involves atomically thin layers of materials placed on top of each other. Rotating or twisting one or more layers at a slight angle creates a unique pattern. A moiré pattern also affects the behavior of electrons. „This changes the spectrum of energy levels available to electrons and can provide the conditions for interesting phenomena to arise,” said Sergio C., one of the four co-first authors of the latest paper. De la Barrera says. De la Barrera, who conducted the work while a postdoc at MIT, is now an assistant professor at the University of Toronto.

A moiré structure can also be tailored to different behaviors by changing the number of electrons added to the system. As a result, the field of twisttronics has exploded over the past five years as researchers around the world have used them to create new atomically thin quantum materials. Examples from MIT alone:

• Turning a moiré material called magic-angle twisted bilayer graphene into three different — and useful — electronic devices. (Among the scientists involved in that work, reported in 2021, is Daniel Roden-LeGrain, co-first author of the current work and an MIT postdoc in physics. They were led by Jarillo-Herrero.)
• A new property in a well-known family of semiconductors is engineering ferroelectricity. (The scientists involved in that work, announced in 2021, were led by Jarillo-Herrero.)
• Predicting exciting new magnetic phenomena, complete with a „recipe” for realizing them. (Scientists involved in that work, Announced in 2023, including MIT physics professor Liang Fu and MIT graduate student in physics Nisarka Pal. Fu and Paul are co-authors of the current paper.)

Towards new quasicrystals

In the current work, the researchers tinkered with a moiré structure made up of three sheets of graphene. Graphene is made of a single layer of carbon atoms arranged in a honeycomb-like structure. In this case, the team stacked three sheets of graphene on top of each other, but twisted the two sheets at slightly different angles.

To their surprise, the system produced a quasicrystal, an unusual type of material discovered in the 1980s. As the name suggests, quasicrystals are somewhere between a crystal like diamond, which has a regular continuous structure, and an amorphous material like glass, where „the atoms are all aligned, or arranged randomly,” says de la Barrera. In short, de la Barrera says, quasicrystals „have really strange shapes” (see some examples Here)

However, compared to crystals and amorphous materials, less is known about quasicrystals. This is in part because they are difficult to make. „It doesn’t mean they’re not interesting; it just means we don’t pay much attention to them, especially in their electronic properties,” says de la Barrera. A relatively simple new platform could change that.

More learning

Since the original researchers were not experts in quasicrystals, they turned to someone else: Professor Ron Lifshitz of Tel Aviv University. Aviram Uri, one of the paper’s co-first authors and an MIT Pappalardo and VATAT postdoctoral fellow, was Lifshitz’s student during his undergraduate studies in Tel Aviv and was aware of his work on quasicrystals. Lifshitz is also a teacher Nature The paper helped the team better understand what they were seeing, which they called moiré quasicrystals.

Physicists then modified a Moiré quasicrystal to make it superconducting, or conducting current without resistance below a certain low temperature. This is important because superconducting devices can transfer current through electronic devices much more efficiently than is possible today, but this phenomenon is not yet fully understood in all cases. The new moiré quasicrystal structure brings a new way to study it.

The team also found evidence of symmetry breaking, another phenomenon that „suggests that electrons interact very strongly with each other. As physicists and quantum matter scientists, we want our electrons to interact with each other because that’s where the fascinating physics happens,” de la Barrera says.

Ultimately, „we’ve been able to understand the subject through discussions across continents, and we believe we have a good handle on what’s going on now,” Urie says, although „we still don’t fully understand the system. There are still some mysteries.”

The best part of the research is „solving the puzzle of what we’ve actually created,” de la Barrera says. „We expected [something else]So it was a very pleasant surprise when we realized that we were actually looking at something very new and different.

“I have the same answer,” says Yuri.

Additional teachers Nature The paper was written by MIT physics professor Raymond C. Assyria; Mallika D. Randeria, a researcher at MIT Lincoln Laboratory who served as a Pappalardo Fellow at MIT and was another co-first author of the paper; Trideep Devakul, an assistant professor at Stanford University and a postdoc at MIT; Philip JD Crowley, postdoctoral fellow at Harvard University; and Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan.

This work was funded by the US Army Research Office, the US National Science Foundation, the Gordon and Betty Moore Foundation, the MIT Pappalardo Fellowship, the VATAT Outstanding Postdoctoral Fellowship in Quantum Science and Technology, JSPS KAKENHI, and the Israel Science Foundation.